Photosensitive prepolymer composition and method



April 2, 1968 M. N. GIANGUALANO ETAL PHOTOSENSITIVE PREPOLYMER COMPOSITION AND METHOD Original Filed Oct. 10, 1962 M57344 CL 40 A p; y eE /fr :04 77A/6 EEMOI Z eff/f7 7 /200614 Mar/4 ArraemE/ United States Patent ()fiice 3,376,139 Patented Apr. 2, 1968 3,376,139 PHOTOSENSETIVE PREPOLYMER COMPOSITION AND METHOD Michael N. Giangualano, now by judicial change of name Michael Nicholas Gilano, 1718 W. Chalet Ave., Anaheim, Calif. 92804; Irvin W. Martenson, 16615 Pequeno Place, Pacific Palisades, Calif. 90272; and Lawrence H. Ott, 1245 E. Altadena Drive, Altadena, Calif. 91001 Continuation of application Ser. No. 229,605, Oct. 10, 1962. This application Feb. 1, 1966, Ser. No. 539,236

12 Claims. (Cl. 9635.1)

The present invention is a continuation of copending application entitled, Photosensitive Prepolymer Composition and Method, Ser. No. 229,605, filed in the name of the same inventors on Oct. 10, 1962, now abandoned.

The present invention relates to the photosensitization of prepolymer compositions, and more particularly to chemical compositions for making photographic relief images of particular use in the graphic arts, such as for printing plates, printed circuit boards, name plates, chemical milling, etc.

It is well known in the art of photo-mechanical reproduction how to utilize various materials such as bichromated shellac, polyvinyl alcohol, polyvinyl cinnamate, and related unsaturated polymers to form resist images upon various substrates or supports such as copper, copper-clad plastic sheets, aluminum, steel, brass, bronze, and othre metals; and also on glass and plastics.

Bichromated shellac, chromated polyvinyl alcohols, and chromated polyvinyl butyrals have limited shelf life, and the bichromate sensitizer must be stored in a separate container and mixed with the film-forming polymer just prior to use.

Polyvinyl cinnamate and related unsaturated ester polymers undergo film shrinkage during overexposure to actinic light, and, therefore, have certain limitations for fine-detail work.

There is a need for photosensitive compositions which are characterized by improved detail, better chemical resistance, long storage life, reproducibility from batch to batch, being preparable as a one-package system, and ease of removal after etching. There is also a need for photosensitive film compositions which do not appreciably shrink when exposed to actinic rays and which can be repeatedly washed and etched as required without adverse effects to the image detail or undercutting of the relief image.

It is an object of the present invention, therefore, to provide a novel photosensitive polymer resist.

It is another object of the present invention to provide a method for the photosensitization of prepolymers.

It is still another object of the present invention to provide a photosensitive composition which can be packaged in a single container with the required photo initiator and which has a long shelf life and exhibits unique chemical, physical, and electrical properties.

Another object of the present invention is to provide a photosensitive composition which can be easily removed by dipping in a solvent for several minutes and wiping it off.

Another object of the present invention is to provide a stable photosensitive composition which requires no blending, heating, or chemical treatment before use, which can be exposed to light rays over a Wide spectral range, and which permits metals and other objects to be precoated and stored for long periods before and after exposure.

Another object of the present invention is to provide a superior stable light-sensitive composition which can be cross linked under the influence of actinic rays and which will form a durable coating having good heat resistance,

low moisture absorption, and high resistance to acids, alkalis, and organic solvents.

According to one embodiment of the present invention, a prepolymer of an aryl allyl ester having two or more allyl groups is combined 'with an initiator or sensitizing agent and dissolved in a suitable solvent. The term aryl allyl ester is herein defined to include polynuclear allyl esters and aryl allyl ester copolymers, in addition to aryl allyl esters having only a single aryl group.

The sensitizing agent must be one that absorbs actinic radiation so as to dissociate into free radicals which accelerate complete polymerization of the prepolymer. The sensitizing agent can be ethers of benzoin, such as methyl, ether of benzoin; p,p-substituted benzophenones such as 4,4'-bis(dimethylamine) benzophenone and 4,4'-bis(di ethylamine) benzophenone; or his l-anthraquinonyl amino anthraquinones such as 1,4 bis(1-anthraquinoyl amino) anthraquinone and 1,5 bis(l-anthraquinonyl amino) anthraquinone, and combinations thereof. Other useful sensitizing agents include polynuclear quinones such as 1,2-benzanthraquinone and 2 methyl anthraquinone; mononuclear quinones such as 2,5-diphenyl-pquinone; aromatic a-diketones such as benzil; substituted aryl methylene dioxy compounds such as piperonal, piperoin, 3,4-methylene dioxychalcone, and 5,6-methylene dioxyhydrindone-l; substituted fi-naphthoselenazolines such as l-methyl-Z-acetyl methylene ,3 naphthoselenazoline; substituted B-benzothiazolines such as 3-methyl-2-benzoyl methylene benzothiazoline; substituted S-naphthothiazolines such as 1-methyl-2-menzoyl methylene-B-naphthothiazoline; anthrones such as anthrone; benzanthrones such as benz-Z-ethylbenzanthrone and 7-H-benz(de)-an thracen-7-one; and azabenzanthrones such as 2-keto-3- methyl-1,3-diazabenzanthrone.

By the term prepolymer, as used herein, is meant an intermediate stage in the reaction of a thermosetting resin, which stage is similar to B-staged epoxy resins. That is, the prepolymer, which is soluble, is a monomer polymerized to partial completion. By combining the prepolymer of the present invention with a proper sensitizing agent, dissolving it in a suitable solvent, and eposing the combination to actinic radiation, the polymerization is completed to form a thermoset, irreversible, infusible, solid.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is an isometric view of a laminated metalclad board.

FIGURES 2-6 are sectional views taken through the board of FIGURE 1, and showing successive steps in the use of the photosensitive resist composition according to the present invention.

The prepolymers of aryl diallyl esters can be prepared by controlled partial polymerization of the monomeric aryl diallyl ester. For example, the diallyl isophthalate liquid monomer is converted to the prepolymer by heating the liquid daillyl isophthalate in a suitable solvent such as xylene in the presence of a peroxide catalyst, and by not allowing the polymerization to proceed to completion. The polymerization is stopped when practically all the change in specific gravity has taken place, preferably to an iodine number of 56 to 58. The reaction is stopped at this point by cooling and the addition of a hydroquinone inhibitor. The prepolymer is then recovered from the solvent and is washed and dried, A white powdered resin is obtained which when dissolved in a suitable solvent yields a water-white solution.

The photosensitive resin composition can be a solid mixture of materials, as in a dried coating, or a solution of the materials in a suitable organic solvent or mixture of solvents. Good solvents for the sensitized aryl allyl prepolymers include:

(1) Esters such as isobutyl acetate, butyl carbitol acetate, amyl acetate, butyl cellosolve acetate, ethyl acetate, and methyl cellosolve acetate.

(2) Ketones such as acetophenone, diacetone alcohol, diisobutyl ketone, methyl isobutyl ketone, and isophorone.

(3) Glycol ethers such as ethylene glycol methyl ether, diethylene glycol methyl ether, and propylene glyco methyl ether.

(4) Aromatic solvents such as benzene, toluene, and xylene.

(5) Chlorinated solvents such as 1,1,1-trichlorethane, trichlorethylene, and methylene chloride.

The described prepolymer resin has the rare characteristic that its polymerization can be stopped at a determined point and it can be precipitated as a solid and stored for an indefinite period at ambient temperatures, and if desired, converted at any time into an infusible solid by employing peroxides and heat and pressure, or in accordance with this invention, by means of actinic radiation.

The resultant diallyl isophthalate prepolymer exhibits film-forming properties, excellent chemical resistance to 'both acids and alkalis, excellent moisture and heat resistance, and shows very little shrinkage when further cross-linked with actinic light. As a result of these properties, it is an ideal material for use as a resist in the manufacture of printed circuit boards and semiconductors, and in microchemical milling.

The light-sensitive polymeric composition, by being preshrunk before use, makes it possible to obtain accurate dimensional detail in printed circuits, chemical milling, etc., since a minimum shrinkage will occur during the further cross-linking of the aryl allyl ester prepolymer when it is exposed to actinic rays. This is because of the fact that the aryl allyl ester prepolymers have been previously processed to the point where practically all of the change in specific gravity has taken place, thereby assuring that very little shrinkage will occur during exposure to actinic radiation. This means that for fine detail work, the shrinkage does not have to be compensated for in the photographic negative.

Another advantage is the fact that the prepolymer can be dissolved in a suitable organic solvent along with the sensitizers considerably in advance of exposure, and will exhibit excellent shelf life under non-ideal conditions of temperature.

The prepolymers of aryl diallyl, aryl triallyl, aryl tetra allyl and polynuclear dialyl esters exhibit excellent light sensitivity and can be sensitized to increase their reactivity to actinic rays as much as 100 to 200 times. When sensitizer compounds are added to the prepolymeric aryl allyl esters, they exhibit exceptional stability, and therefore have long shelf life.

The concentration of sensitizer in the photo resist composition depends upon the amount of sensitive polymeric compound, i.e., the aryl allyl prepolymer, present. In the case of the prepolymer of diallyl isophthalate, from about 1 to 20%, preferably 1.5 percent by weight, of 1,4 bis(l-anthraquinoyl amino) anthraquinone can be used. Some sensitizers such as p,p' substituted benzophenones, e.g., 4,4-bis(dimethylamino) benzophenone, in an amount less than 1.5%, cause a considerable increase in sensitivity to actinic light. The sensitizer is excited by the actinic radiation, and, in turn, speeds up the polymerization. This is accomplished by the sensitizer being dissociated into free radicals by the actinic radiation or energy that it absorbs. The free radicals initiate the polymerization of the prepolymer.

The present invention will be more readily understood from a consideration of the following specific examples, which are given for the purpose of illustration only, and are not intended to limit the scope of the invention in any way:

Example I A typical resist formulation useful for making relief images on copper plates or printing plates is prepared as follows:

Grams Diallyl isophthalate prepolymer 1.5 Methyl isobutyl ketone 2.5 Cellosolve acetate 2.5 Methyl ether of benzoin 0.24

2.4 grams of a prepolymer of an aryl allyl ester, such as diallyl isophthalate, the preparation of which has been described herein, is dissolved in a mixture of 5.0 grams of methyl isobutyl ketone and 5.0 grams of cellosolve acetate with slight heat and agitation. Then 0.10 gram I of benzil and 0.01 gram of p,p-dimethyl amino benzophenone is added directly to the solvent resin solution and mixed until dissolved. After filtering, the composition is ready for use.

No special order of. dissolving the materials .is required, and when the solution is obtained and filtered, it is ready for use.

Example III Grams Diallyl isophthalate prepolymer 1.5

Methyl isobutyl ketone 5.0

4,4 bis(dimethylamino) benzophenone 0.01

Example IV Grams Triallyl trimellitate prepolymer 1.5

Cellosolve acetate 5.0

4,4 bis(dimethylamino) benzophenone 0.01,

Example V Grams Tetra allyl pyromellitate prepolymer 1.5

Xylene 2.5

Isopropylacetate 2.5

4,4 bis(dimethylamine) benzophenone -s 0.01

The aryl allyl prepolymers are interchangeable in the photo resist composition and can be sensitized by the same initiators. For the sake of further examples of sensitizers, diallyl isophthalate will be used, but it is. not

intended to restrict the mentioned sensitizers to the pre- 6 Example VIII elevated temperature in subdued light, the plate is placed Grams in intimate contact with a photographic negative and Diallyl isophthalate prepolymer 1.5 exposed to actinic light. Useful light sources are mercury Methyl isobutyl ketone 5.0 vapor lamps or high-ampere white-flame arcs. Exposure 1,2-benzanthraquirione 0.05 5 times vary from a fraction of a minute to several minutes at a distance of 2 to 3 feet, respectively. The exposed Examp 16 IX Grams plate is then developed by immersion in an organic solvent Dianyl isophthalate Prepolymer 15 such as methyl ethyl ketone or 1,l,l-trichlorethane for Cellosolvg acetate 20 less than a minute at room temperature. During develop- Diacetone alcohol 3 0 10 ment theorganic solvent dissolves the unexposed areas of 2 th 1 th thes coating and allows the exposed areas to remain intact y an raqumone on the support plate. The transparent image on the photo- Example X graphic negative is thus accurately reproduced as a resist Grams image on the support plate. Diallyl isophthalate prepolymer 1.5 After development, an optional step is to dye the resist Methyl isobutyl ketone 2.0 image, which is normally transparent and colorless and Cellosolve acetate 2.0 difiicult to see, by immersion for less than a minute in a Toluene 1.0 dye bath comprising a synthetic dye in a compatible Piperonal 0.15 organic solvent. Finally, the plate is washed in flowing water and dried. Examp 1e XI Grams I ftetching ofdthe miettall balset areas not prgt ected by Elie res1s image is esire e p a e is immerse in a suita e 32253 z g s ig i gs gg n acid or alkali. Ferric chloride and ammonium persulfate are common etchants for copper; sodium hydroxide is g gg used for aluminum, as is also electrolytic etching in dllllle 2 keto 3 methy1 1 g g ggg gggg g; 6 hydrochloric acid. In other processes the resist image serves as an intermediate step for electroplating and Example XII evaporative-film operations, or as an opaque film for Grams images on transparent objects as signs, or to produce Diallyl isophthalate prepolymer 1.5 decorative effects. In photo milling, which is a relatively Methyl isobutyl ketone 2.0 new method for making small accurate metal parts of Xylene 2.0 thin metal sheet, the resist image is applied to both sides Cellosolve acetate 1.0 of the sheet in accurate register. The metal etchant i l-methyl-z-benloyl methylefle-fi-naphthothialoline then applied to both sides to remove unwanted metal. The probable structure of the recurring units of the Turning f to the i f which illustrate the use prepolymers f aryl n esters can be better understood of the described photosensitive resist composition in a from the following example process for making printed circuit boards, FIGURE 1 (1) Prepolymer of diallyl isophthalate shows a board 11 having a covering layer 12 of 0.0014 (CH-CH2OOC OCOOCH2(H3H IIs (E CH2 0oooHioH-oI-I-CHioO L H3 CH3 N (2) Prepolymer of triallyl trimellitate inch thick copper sheet laminated to a 0.060 inch thick CH phenolic composition base 13, such as is commonly H 2 used in the printed circuit industry. Board 11 should be 0133 "COOCHrCH scrubbed with an abrasive cleaner and dried. FIGURE 2 is a sectional view showing board 11 after I the described photosensitive resist composition is applied a -co0oH,-orr o as by flowing onto the surface of copper layer 12 to form a N layer 14. The excess resist can be drained by holding the 2 board vertically for several minutes. The coating is then (3) Prepolymer of tetra-allyl pyromellitate dried by placing board 11 in an oven maintained at CH2 CH3 CH3 CH2 iiHCHi0oc -CoooHi0HoHoH0oC -ooooHi( iH CH-OHOOO COOCH2-CH HCCH2OOC- COOCH2CH Ha I H2 (3H2 (13H; N

(4) Prepolymer of a diallyl ester of a polynuclear approximately 150 F. for 10 minutes. The coating, when dicarboxylic acid, e.g., the prepolymer of diallyl anthralate removed from the oven, is smooth, glossy, and hard.

L CH3 CH3 CH3 CH2 The method of preparing a support plate with a photo- 7 FIGURE 3 shows how mask 15, which can be a photopolyrnerizable coating composition includes the following graphic negative of an electrical circuit, is placed in steps: the photosensitive material is applied to the support contact with the photosensitive layer 14. The combination plate by dipping, spraying, or roller coating. The wet is then put into the vacuum frame of a printing machine coated plate is commonly drained or whirled to obtain and exposed for one to three minutes to a 35-ampere a uniform film thickness. After drying at room or slightly white-flame are light source about 2 feet away, represented by arrows 21. Light of from 3200-4100 angstrom units is very satisfactory. After expasure, the board is removed and the coating developed by placing the board vertically in a tank of methyl ethyl ketone for approximately 30 seconds. The board is then removed and immersed for 30 seconds in a second tank containing a solution of dye in organic solvent to render the normallytransparent resist image visible.

FIGURE 4 shows the board after it is rinsed in flowing water to remove adhering dissolved resist solution and excess dye and finally dried by slightly warming it.

The board at this stage is ready for etching and his on the copper surface the image of the electrical circuit, this image being comprised of a film of dry, hard, polymerized resist. The surface area other than that covered by the resist image is bare copper.

FIGURE 5 shows the board after the bare copper is removed by a suitable acid-type etchant. The board can be placed in a spray-type etching machine, of a kind commonly used in the industry, which sprays a solution of ferric chloride on the surface. The concentration of the ferric chloride, commonly stated in terms of specific gravity, can be 38 degrees Baum. Within several minutes the bare unprotected copper on the board surface will be completely etched away. The board is then removed and thoroughly rinsed to remove all traces of ferric chloride, and then dried.

FIGURE 6 shows the board after it is immersed in a solvent such as trichlorethylene or methyl ethyl ketone to soften the resist image, which can be removed by scrubbing with a mild abrasive cleaner, revealing the brightcopper electrical circuit. The finished circuit board can be rinsed in hot water and dried.

There has thus been described how certain polymeric material compositions and elements embodying a prepolymer of aryl allyl esters, and which exhibit some light sensitivity, such as prepolymers of aryl triallyl esters, prepolymers of aryl tetra allyl esters, and prepolymers of polynuclear diallyl and triallyl esters, and in particular the prepolymers of iso and para aryl diallyl esters, such as prepolymers of diallyl isophthalate, and the prepolymers of diallyl terephthalate, and certain sensitizers which increases the light sensitivity of this class of compounds, can be used in the manufacture of printed-circuit boards.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. A photosensitive resist composition consisting essentially of:

(a) a prepolymer of an aryl allyl ester having more than one allyl group, said prepolymer being a solvent-soluble material which is a solid at ambient temperature, and which undergoes very little shrinkage when further cross'linked by actinic radiation, and

(b) a photopolymerization sensitiving agent which, upon absorbing actinic radiation at room temperature accelerates polymerization of said prepolymer.

2. A composition as defined in claim 1 in which said prepolymer has been recovered from the reaction mixture produced by polymerization of monomer.

3. A composition as defined in claim 1 in which said prepolymer has been recovered from the reaction mixture produced by partial polymerization of monomer from which said prepolymer has been prepared.

4. A composition as defined in claim 1 in which said prepolymer has been separated from the reaction mixture produced by polymerization of monomer from which said prepolymer has been prepared.

5. A composition as defined in claim 1 in which said prepolymer has been precipitated from the reaction mix-- I sensitizing agent is selected from the group consisting of methyl ether of benzoin, 4,4 bis(dimethylamino)benzophenone, 4,4 bis(diethylamino)benzophenone, 1,4 bis(1- anthraquinoyl amino) anthraquinone, 1,4, bis(1-anthra quinoyl amino) anthraquinone, 1,2 benzanthraquinone, 2 methyl anthraquinone, 2,5-diphenyl-p-quinone, benzil, piperonal, 3,4-methylene dioxychalcone, 5,6-methylene dioxhydrindone-l, piperoin, l-methyl-Z-acetyl methylene-{3- naphthoselenazoline, 3-methyl-2-benzoyl methylene benz othiozoline, 1-methyl-2-benzoyl methylene-fi-naphthothiazoline, anthrone, benz-Z-ethylbermanthrone, 7-H-benz- (de)-anthracen-7-one, and 2-keto-3-methyl-1,3-diazabenzanthrone.

8. A composition as defined in claim 2 in which said prepolymer is selected from the group consisting of aryl diallyl esters, aryl triallyl esters, aryl tetra allyl. esters, polynuclear polyallyl esters, and aryl polyallyl ester copolymers.

9. A composition as defined in claim 2 in which said prepolymer is selected from the group consisting of diallyl isophthalate, diallyl terephthalate, diallyl anthralate, triallyl trimellitate and tetra allyl pyromellitate.

10. A composition as defined in claim 2 in which said prepolymer is diallyl isophthalate.

11. A method of photographically printing animage upon a surface, consisting essentially of the steps of:

(a) applying to said surface a photopolymerizablelayer comprising a photopolymerization sensitizing agent and a prepolymer selected from the group consisting of aryl diallyl esters, aryl triallyl esters, aryl tetra allyl esters, polynuclear polyallyl esters, and aryl polyallyl ester copolymers, said prepolymer being capable of polymerizing to completion by photoinitiated polymerization in the presence of said sensitizing agent which is activatable by actinic radiation, said prepolymer being a solvent-soluble material which is a solid at ambient temperature, has been recovered from the reaction mixture produced by polymerization of monomer and undergoes very little shrinkage when further cross-linked by actinic radiation,

(b) drying said layer,

(0) photopolymerizing said layer with said actinic radiation through an image-bearing transparency placed in contact with said layer and having substantially opaque and substantially transparent areas, until.

substantially complete polymerization of said prepolymer occurs throughout the entire thickness of said layer in the areas thereof corresponding to said substantially transparent area, whereby said layer in said corresponding areas is converted to the thermoset, irreversible, infusible, solid state, but without any substantial polymerization in the areas of said layer corresponding to said substantially opaque areas, and r (d) removing said layer in the latter corresponding areas.

12. Photosensitive photographic means including a support surface having thereon a dry photopolymerizable layer consisting essentially of:

(a) a photopolymerization sensitizing agent which is activatable by actinic radiation, and

9 10 (b) a prepolymer of an aryl allyl ester having more 2,791,504 5/1957 Plambeck.

than one allyl group, said prepolymer being capable 2,832,758 4/1958 Heiburger et al. 26078.4 of polymerizing to completion by photoinitiated po- 3,030,341 4/1962 Willard 260-78.4 lymerization in the presence of said sensitizing agent, 3,036,915 5/ 1962 Notley 96--115 XR and being a solvent-soluble material which is a solid 5 3,060,025 10/1962 Burg et al. 96116 XR at ambient temperature, has been recovered from the OTHER REFERENCES reaction mixture produced by polymerization of monomer and undergoes very little shrinkage When Nichols, and Flowers, IIld- & g

further cross-linkecl by actinic radiation. 1950, P g

Referen e Cit d 10 J. TRAVIS BROWN, Acting Primary Examiner. UNITED STATES PATENTS NORMAN G. TORCHIN, Examiner. 2,339,058 1/1944 DeAlelio 260-784 R. SMITH, Assistant Examiner.

2,722,512 11/1955 Crandall. 

1. A PHOTOSENSITIVE RESIST COMOSITION CONSISTING ESSENTIALLY OF: (A) A PREPOLYMER OF AN ARYL ALLYL ESTER HAVING MORE THAN ONE ALLYL GROUP, SAID PREPOLYMER BEING A SOLVENT-SOLUBLE MATERIAL WHICH IS A SOLID AT AMBIENT TEMPERATURE, AND WHICH UNDERGOES VERY LITTLE SHRINKAGE WHEN FURTHER CROSS-LINKED BY ACTINIC RADIATION, AND (B) A PHOTOPOLYMERIZATION SENSITIVING AGENT WHICH, UPON ABSORBING ACTINIC RADIATION AT ROOM TEMPERATURE ACCELERATES POLYMERIZATION OF SAID PREPOLYMER. 